As early as 1985, medical literature documented a relationship between decreased core body temperature and increased bodily activity in heart failure patients. In a paper by Stanley A. Rubin (RUBIN, STANLEY A. Core body temperature regulation of heart rate during exercise in humans. J. Appl. Physiol. 62(5): 1997–2001, 1987), a significant correlation was found between an observed change in core body temperature and heart rate changes in heart failure patients. Rubin defined core body temperature as the mixed venous blood pool found in the pulmonary artery. Using a thermistor mounted on the distal end of a Swan-Ganz catheter, Rubin found that the core body temperature of heart failure patients decreased during exercise, while the core body temperature in normal patients typically increased during exercise.
This relationship between core body temperature and heart activity has been observed in other studies. In a paper by Frank G. Shellock, et al. (SHELLOCK, FRANK G., H. J. C. SWAN, AND STANLEY A. RUBIN. Muscle and femoral vein temperatures during short term maximal exercise in heart failure. J. Appl. Physiol. 58(2): 400–408, 1985), reductions in core body temperatures in heart failure patients were observed while the heart failure patients underwent exercise. Shellock, et al. concluded that the core body temperature decrease observed in heart failure patients is partially caused by the re-distribution of cooler blood from the underperfused skeletal muscles into the core blood during exercise. Another paper by Shellock and Rubin (FRANK G. SHELLOCK AND STANLEY A. RUBIN. Mixed venous blood temperature response to exercise in heart failure patients treated with short-term vasodilators. Clinical Physiology 5, 503–514, 1985), also concluded that the core body temperature drop was due to circulatory inadequacies. This conclusion was based on Shellock's and Rubin's conclusion that heart failure patients treated with vasodialators experience an attenuation of the core body temperature response typical during exercise, as a result of vasodialator-induced improvement in circulation.
More recent research ascribes the drop in core body temperature to low blood pH levels. As a heart failure patient exercises, the heart failure patient experiences an increase of CO2 in its blood as the blood attempts to eliminate the CO2 from the exercising muscles. The heart failure patient will normally increase its breathing volume in an attempt to evacuate the increased level of CO2 from the blood. However, in heart failure patients, the blood system cannot deliver the blood to the lungs fast enough to support an adequate CO2 for O2 exchange in the lungs. It is well known that higher levels of CO2 correlate with lower levels of blood pH. As CO2 accumulates in the heart failure patient's body, the blood's pH level drops. Because pH is a catalyst for virtually every chemical reaction in the body, the heart failure patient's chemical reactions will be slowed by the reduced pH levels. As the blood's pH level drops with the increased CO2 levels, the heart failure patient's bodily chemical reactions responsible for heat production during exercise are slowed and the core body temperature stays flat or decreases.
While the core body temperature drop phenomenon has been documented in the literature described above, little has been done to apply this knowledge to benefit heart failure patients. A heart failure patient may require immediate medical attention or an alteration of medical treatment in certain conditions where an increase in heart activity and a decrease in core body temperature are coincident.
Therefore, there is a need in the art for a core body temperature monitoring system that can determine when the core body temperature level of a heart failure patient is outside of an acceptable range. The monitoring system also should determine whether the relationship between the core body temperature level and the activity of the heart failure patient is outside of an acceptable range. The monitoring system should be capable of generating an alarm when an unacceptable level has been detected. The monitoring system also should be able to transmit an alarm to a remote location.